const StringDecoder = require('string_decoder').StringDecoder;
const decoder = new StringDecoder('utf8');

const buf = Buffer.from("中文字符串");
for(let i = 0; i < buf.length; i += 5){
    const b = Buffer.allocUnsafe(5);
    buf.copy(b, 0, i);
    console.log(b.toString());
}

console.log("========");

for(let i = 0; i < buf.length; i += 5){
    const b = Buffer.allocUnsafe(5);
    buf.copy(b, 0, i);
    console.log(decoder.write(b));
}